autodialers?  thats not realy so great.  when there is spywhere, there is a trojan.  i have learned that the hard way.

that scene isnt tooooo complicated.   but the fan thingy is a bit complicated,  try turning it off and seeing what happens.  

or... try using yafray,  you might get better results and faster speed.  or kerkythea, or sunflow (particularly fast)

however,  there are something that might supprisingly be a nasty.  check for overlapping verticies,  if two meshes are placed ontop of each other tooo perfectly,  it could cause problems, no idea why, but i've seen it happen.